Re: [PATCH] scsi:NCR5380: remove same check condition in NCR5380_select

From: Finn Thain
Date: Thu Aug 02 2018 - 22:55:59 EST

On Thu, 2 Aug 2018, Michael Schmitz wrote:

> This redundant load of the ICR has been in the driver code for a long
> time. There's a small chance it is intentional,

Actually, it is intentional.

> so at least minimal testing might be in order.

Minimal testing is almost useless if you are trying to prove the absence
of race conditions. SCSI arbitration is a race between targets by design;
so a race between the CPU and the 5380 is going to be hard to observe.

> Finn - does the ICR_ARBITRATION_LOST bit have to be cleared by a write
> to the mode register?

Something like that: the write to the mode register does clear the
ICR_ARBITRATION_LOST bit, because it clears the MR_ARBITRATE bit.

> In that case, the first load would have been redundant and can be
> omitted without changing driver behaviour?

This code is a faithful rendition of the arbitration flow chart in the
datasheet, so even if you are right, I wouldn't want to change the code.

Besides, I think your argument assumes that ICR and MR are synchronized,
and also assumes that targets are obeying the spec.


> Cheers,
> Michael